Description

Mixed substrata of boulders, cobbles, pebbles and gravel, typically found in tidal rapids with kelp Saccharina latissima and Laminaria hyperborea and red seaweeds. Saccharina latissima usually dominates this habitat although Laminaria hyperborea may occur in equal abundance at some sites. The kelp in these tidal rapids does not form the same dense canopies associated with stable tide-swept bedrock, but generally occurs at lower abundance (Frequent). Other brown seaweeds occur in significant amounts in these tidal rapids including Dictyota dichotoma, Halidrys siliquosa and Chorda filum. These mixed substrata support a greater diversity of species than scoured bedrock narrows (XKT). In particular, there is an increase in red algal species such as Corallina officinalis, Bonnemaisonia hamifera and Ceramium nodulosum, although none occur in any great abundance. Red seaweeds common to both XKT and this biotope include Chondrus crispus,Delesseria sanguinea, Plocamium cartilagineum and Phycodrys rubens. Good examples of this biotope often have maerl gravel (Lithothamnion sp.) or rhodoliths between cobbles and boulders. Where maerl dominates, the biotope should be recorded as a maerl bed (SS.SMP.Mrl). The sponges associated with more stable, tide-swept conditions are generally absent, but the anthozoan Anemonia viridis might be present. Cobbles and pebbles are encrusted by the ubiquitous polychaete Spirobranchus triqueter and provide shelter for scavenging crabs such as Carcinus maenas and the hermit crab Pagurus bernhardus, gastropods such as Gibbula cineraria and echinoderms such as Echinus esculentus, Asterias rubens, Ophiocomina nigra and Ophiothrix fragilis which favour these sites of increased water movement. Additional infaunal species, inhabiting the sediment pockets, include Lanice conchilega and Sabella pavonina, which can be locally abundant.

Depth range

0-5 m, 5-10 m

Additional information

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Further information sources

Sensitivity characteristics of the habitat and relevant characteristic species

IR.MIR.KT.XKT & IR.MIR.KT.XKTX are defined by bedrock reefs and mixed substrata of boulders, cobbles, pebbles and gravel, typically found in strong tidal streams. The community is characterized by mixed kelp canopies of Laminaria hyperborea and Saccharina latissima (syn. Laminaria saccharina). Dense stands of the brown seaweed Halidrys siliquosa can occur within the kelp along with Dictyota dichotoma. Kelp stipes may also support prolific growths of foliose red seaweeds such as Phycodrys rubens, Membranoptera alata, Delesseria sanguinea and Plocamium cartilagineum. The dominance of kelp species can vary between sites however as substrata stability decreases, as in IR.MIR.KT.XKTX, Saccharina latissima becomes the most dominant canopy forming species (Connor et al., 2004).

In undertaking this assessment of sensitivity, an account is taken of knowledge of the biology of all characterizing species in the biotope. There is an abundance of literature for regeneration of mono-specific Laminaria hyperborea beds, however, there is limited research for the recovery of mixed kelp canopies. For this sensitivity assessment, Laminaria hyperborea and Saccharina latissima are the primary foci of research. However, interspecific competition may influence recovery times. It is also recognized that the understory red seaweed communities also define the biotope. Examples of important species groups are mentioned where appropriate.

Resilience and recovery rates of habitat

In favourable conditions, Laminaria hyperborea can recover following disturbance events reaching comparable plant densities and size to pristine Laminaria hyperborea beds within 2-6 years (Kain, 1979; Birkett et al., 1998b; Christie et al., 1998). Holdfast communities may recover in 6 years (Birkett et al., 1998b). Full epiphytic community and stipe habitat complexity regeneration require over 6 years to recover (possibly 10 years). These recovery rates were based on discrete kelp harvesting events and recurrent disturbance occurring frequently within 2-6 years of the initial disturbance is likely to lengthen recovery time (Birkett et al., 1998b, Burrows et al., 2014). Kain (1975a) cleared sublittoral blocks of Laminaria hyperborea at different times of the year for several years. The first colonizers and succession community differed between blocks and at what time of year the blocks were cleared however within 2 years of clearance the blocks were dominated by Laminaria hyperborea.

Laminaria hyperborea has a heteromorphic life strategy, A vast number of zoospores (mobile asexual spores) are released into the water column between October-April (Kain & Jones, 1964). Zoospores settle onto rock substrata and develop into dioecious gametophytes (Kain, 1979) which, following fertilization, develop into sporophytes and mature within 1-6 years (Kain, 1979; Fredriksen et al., 1995; Christie et al., 1998). Laminaria hyperborea zoospores have a recorded dispersal range of approximately 200m (Fredriksen et al., 1995). However, zoospore dispersal is greatly influenced by water movements, and zoospore density and the rate of successful fertilization decreases exponentially with distance from the parental source (Fredriksen et al., 1995). Hence, recruitment following disturbance can be influenced by the proximity of mature kelp beds producing viable zoospores to the disturbed area (Kain, 1979, Fredriksen et al., 1995).

Other factors that are likely to influence the recovery of kelp biotopes is competitive interactions with the Invasive Non-Indigenous Species (INIS) Undaria pinnatifida (Smale et al., 2013; Brodie et al., 2014; Heiser et al., 2014). Undaria pinnatifida has received a large amount of research attention as an INIS which could out-compete UK kelp habitats (see Farrell & Fletcher, 2006; Thompson & Schiel, 2012, Brodie et al., 2014; Hieser et al., 2014). Undaria pinnatifida was first recorded in Plymouth Sound, the UK in 2003 (NBN, 2015) subsequent surveys in 2011 have reported that Undaria pinnatifida is widespread throughout Plymouth Sound, colonizing rocky reef habitats. Where Undaria pinnatifida is present there was a significant decrease in the abundance of other Laminaria species, including Laminaria hyperborea (Heiser et al., 2014). In new Zealand, Thompson & Schiel (2012) observed that native fucoids could out-compete Undaria pinnatifida and re-dominate the substratum. However, Thompson & Schiel (2012) suggested the fucoid recovery of the substratum was partially due to an annual Undaria pinnatifida die back, which as noted by Heiser et al. (2014) did not occur in Plymouth sound, UK. It is unknown whether Undaria pinnatifida will out-compete native macroalgae in the UK. However from 2003-2011 Undaria pinnatifida had spread throughout Plymouth sound, UK, becoming a visually dominant species at some locations within summer months (Hieser et al., 2014). There was limited evidence available to assess the ecological impacts of Undaria pinnatifida on Laminaria hyperborea associated communities. Kelp biotopes are unlikely to fully recover until Undaria pinnatifida is fully removed from the habitat, which as stated above is unlikely to occur.

Saccharina lattissima is a perennial kelp characteristic of wave sheltered sites of the North East Atlantic, distributed from northern Portugal to Spitzbergen, Svalbard (Birkett et al., 1998b; Conor et al., 2004; Bekby & Moy, 2011; Moy & Christie, 2012). Saccharina lattissima is capable of reaching maturity within 15-20 months (Sjøtun, 1993) and has a life expectancy of 2-4 years (Parke, 1948). Maximum growth has been recorded in late winter early spring, in late summer and autumn growth rates slow (Parke, 1948; Lüning, 1979; Birkett et al., 1998b). The overall length of the sporophyte may not change during the growth season due to the marginal (distal) erosion of the blade, but extension growth of the blade has been measured at 1.1 cm/day, with total length addition of over 2.25 m of tissue per year (Birkett et al., 1998b). Saccharina latissima has a heteromorphic life strategy. Vast numbers of zoospores are released from sori located centrally on the blade between autumn and winter. Zoospores settle onto rock substrata and develop into dioecious gametophytes (Kain, 1979) which, following fertilization, germinate into juvenile sporophytes from winter-spring. Kelp zoospores are expected to have a large dispersal range, however, zoospore density and the rate of successful fertilization decreases exponentially with distance from the parental source (Fredriksen et al., 1995). Hence, recruitment following disturbance can be influenced by the proximity of mature kelp beds producing viable zoospores to the disturbed area (Kain, 1979; Fredriksen et al., 1995).

The temperature isotherm of 19-20°C has been reported as limiting Saccharina lattissima growth (Müller et al., 2009). Gametophytes can develop in ≤23°C (Lüning, 1990). However, Bolton & Lüning (1982) reported an experimental optimal temperature of 10-15°C for the growth of the Saccharina latissima sporophyte. Growth was inhibited by 50-70% at 20°C and, all experimental specimens completely disintegrated after 7 days at 23°C. In the field, Saccharina latissima has however shown significant regional variation in its acclimation response to changing environmental conditions. For example, Gerard & Dubois (1988) observed sporophytes of Saccharina latissima which were regularly exposed to ≥20°C could tolerate these high temperatures, whereas sporophytes from other populations which rarely experience ≥17°C showed 100% mortality after 3 weeks of exposure to 20°C. Therefore, the response of Saccharina latissima to a change in temperatures is likely to be locally variable.

In 2002 a large-scale decline of Saccharina latissima was discovered on the Norwegian coast (Moy & Christie, 2012). A subsequent large survey was undertaken between 2004-2009 of 660 sites covering 34,000km of south and west Norway to assess the decline of Saccharina latissima abundance and distribution (Moy & Christie, 2012). The survey indicated an 83% reduction of Saccharina latissima forests across the south Norwegian region of Skagerrak. The west Norwegian coast was less affected, but Saccharina latissima was either absent or very sparse at 38% of sites where it was expected to be abundant. At all sites where Saccharina latissima was sparse, a community of ephemeral macroalgae species was dominant and persisted throughout the study period (2004-2009). Bekby & Moy (2011) modelled the regional decline which indicated a decline of 50.7% of Saccharina latissima from Skagerrak, Norway. Approximately 50% of Europe’s Saccharina latissima is found in Norway (Moy et al., 2006), therefore, despite large discrepancies between the two estimates of Saccharina latissima decline (50.7-83%) the results indicated a significant decline in Saccharina latissima across the region. Moy & Christie (2012) suggested the ephemeral filamentous macroalgae communities represented a stable state shift that had persisted throughout the study period (2004-2009). Although no measurements were made, they suggested that the decline was due to low tidal movement and wave action in the worst affected areas combined with the impacts of dense human populations and increased land run-off multiple stressors such as eutrophication, increasing regional temperature, increased siltation and overfishing may also be acting synergistically to cause the observed habitat shift.

Resilience assessment. Of the two kelp species (Laminaria hyperborea and Saccharina latissima) that characterize IR.MIR.KT.XKT & IR.MIR.KT.XKTX, Laminaria hyperborea is the slowest to recover following disturbance. Laminaria hyperborea can regenerate from disturbance within a period of 1-6 years, and the associated community within 7-10 years. Saccharina latissima has reportedly a rapid recovery rate or regeneration time, following clearance of Strongylocentrotus droebachiensis from ‘urchin barrens’ Saccharina latissima was a rapid colonizer appearing after a few weeks, and can reach maturity within 15-20 months (Birkett et al., 1998b). Due to comparatively slow growth rates resilience estimates are based on Laminaria hyperborea, however, the recovery of Saccharina latissima and the understory red seaweed is accounted for where relevant. Resilience has therefore been assessed as ‘Medium’.

Hydrological Pressures

Kain (1964) stated that Laminaria hyperborea sporophyte growth and reproduction could occur within a temperature range of 0-20°C. Upper and lower lethal temperatures have been estimated at between 1-2°C above or below the extremes of this range (Birkett et al., 1988b). Above 17°C Laminaria hyperborea gamete survival is reduced (Kain, 1964, 1971) and gametogenesis is inhibited at 21°C (Dieck, 1992). It is, therefore, likely that Laminaria hyperborea recruitment will be impaired at a sustained temperature increase of above 17°C. Sporophytes, however, can tolerate slightly higher temperatures of 20°C. Temperature tolerances for Laminaria hyperborea are also seasonally variable and temperature changes are less tolerated in winter months than summer months (Birkett et al., 1998b).

The temperature isotherm of 19-20°C has been reported as limiting Saccharina lattissima growth (Müller et al., 2009). Gametophytes can develop in ≤23°C (Lüning, 1990). The optimal temperature for Saccharina latissima sporophyte growth was 10-15°C (Bolton & Lüning, 1982), while reported growth was inhibited by 50-70% at 20°C and all experimental specimens completely disintegrated after 7 days at 23°C. In the field, Saccharina latissima has however shown significant regional variation in its acclimation response to changing environmental conditions. For example, Gerard & Dubois (1988) found Saccharina latissima sporophytes which were regularly exposed to ≥20°C could tolerate these high temperatures, whereas sporophytes from other populations which rarely experience ≥17°C showed 100% mortality after 3 weeks of exposure to 20°C. Therefore, the response Saccharina latissima to a change in temperatures is likely to be locally variable.

Andersen et al. (2011) transplanted Saccharina latissima in the Skagerrak region, Norway and from 2006-2009. There was annual variation, however, high mortality occurred from August-November within each year of the experiment. In 2008 of the original 17 sporophytes 6 survived from March-September (approx. 65% mortality rate). All surviving sporophytes were heavily fouled by epiphytic organisms (estimated cover of 80 & 100%). Between 1960-2009, sea surface temperatures in the region have regularly exceeded 20°C and so has the duration which temperatures remain above 20°C. High sea temperatures have been linked to the slow growth of Saccharina latissima which is likely to decrease the photosynthetic ability of, and increase the vulnerability of Saccharina latissima to epiphytic loading, bacterial and viral attacks (Anderson et al., 2011). These factors combined with the establishment of annual filamentous algae in Skagerrak, Norway are likely to prevent the establishment of self-sustaining populations in the area (Anderson et al., 2011; Moy & Christie, 2012).

Sensitivity assessment. A 2°C increase for one year may impair Laminaria hyperborea recruitment processes and Saccharina latissima sporophyte growth but otherwise not affect the characterizing species. A 5°C increase for one month combined with high UK summer temperatures is likely to affect Laminaria hyperborea sporophyte growth. Saccharina latissima populations that are not acclimated to >20°C may incur mass mortality within 3 weeks of exposure. Resistance has been assessed as ‘Low’, to reflect the potential mass mortality effect of sudden temperature increases on Saccharina latissima, and resilience as ‘High’. Sensitivity has been assessed as ‘Low’.

Kain (1964) stated that Laminaria hyperborea sporophyte growth and reproduction could occur within a temperature range of 0-20°C. Upper and lower lethal temperatures have been estimated at between 1-2°C above or below the extremes of these ranges (Birkett et al., 1988b). Saccharina lattissima has a lower temperature threshold for sporophyte growth at 0°C (Lüning, 1990). Subtidal red algae can survive at temperatures between -2 °C and 18-23 °C (Lüning, 1990; Kain & Norton, 1990).

Sensitivity assessment. Both Laminaria hyperborea and Saccharina latissima have northern distributions (Birkett et al., 1998b). An acute or long-term decrease in temperature within the UK, at the benchmark level, is not likely to have any dramatic effect on biotope structure. Resistance has been assessed as ‘High’, resilience as ‘High’ and sensitivity as ‘Not sensitive’.

Lüning (1990) suggest that ‘kelps’ are stenohaline, their general tolerance to salinity as a phenotypic group covering 16-50 psu over a 24 hr period. Optimal growth probably occurs between 30-35 psu and growth rates are likely to be affected by periodic salinity stress. Birkett et al. (1998b) suggested that long-term increases in salinity may affect Laminaria hyperborea growth and may result in loss of affected kelp, and therefore loss of the biotope.

Karsten (2007) tested the photosynthetic ability of Saccharina latissima under acute 2 and 5 day exposure to salinity treatments ranging from 5-60 psu. A control experiment was also carried at 34 psu . Saccharina latissima showed high photosynthetic ability at >80% of the control levels between 25-55 psu. The effect of long-term salinity changes (>5 days) or salinity >60 PSU on Saccharina latissima’ photosynthetic ability was not tested.

Sensitivity assessment. The evidence suggests that Saccharina latissima can tolerate exposure to hypersaline conditions of ≥40‰. However, optimal salinities for Laminaria hyperborea growth are assumed to be 30-35 psu. Hence, increases in salinity to >40‰ may cause mortality for Laminaria hyperborea. Resistance has been assessed as ‘Low’, resilience as ‘Medium’. The sensitivity of this biotope to an increase in salinity has been assessed as ‘Medium’.

Lüning (1990) suggest that ‘kelps’ are stenohaline, their general tolerance to salinity as a phenotypic group covering 16 - 50 psu over a 24 hr period. Optimal growth probably occurs between 30-35 psu and growth rates are likely to be affected by periodic salinity stress. Birkett et al. (1998) suggest that long-term changes in salinity may result in loss of affected kelp. Hopkin & Kain (1978) tested Laminaria hyperborea sporophyte growth at various low salinity treatments. The results showed that Laminaria hyperborea sporophytes could grow ‘normally’ at 19 psu, growth was reduced at 16 psu and did not grow at 7 psu.

Karsten (2007) tested the photosynthetic ability of Saccharina latissima under acute 2 and 5 day exposure to salinity treatments ranging from 5-60 psu. A control experiment was also carried at 34 psu . Saccharina latissima showed high photosynthetic ability at >80% of the control levels between 25-55 psu. Hyposaline treatment of 10-20 psu led to a gradual decline of photosynthetic ability. After 2 days at 5 psu, Saccharina latissima showed a significant decline in photosynthetic ability at approx. 30% of control. After 5 days at 5 psu, Saccharina latissima specimens became bleached and showed signs of severe damage. The effect of long-term salinity changes (>5 days) or salinity >60 PSU on Saccharina latissima’ photosynthetic ability was not tested. The experiment was conducted on Saccharina latissima from the Arctic, and the authors suggest that at extremely low water temperatures (1-5°C) macroalgae acclimation to rapid salinity changes could be slower than at temperate latitudes. It is, therefore, possible that resident Saccharina latissima of the UK maybe be able to acclimate to salinity changes more effectively and quicker.

Sensitivity assessment. IR.MIR.KT.XKT & IR.MIR.KT.XKTX are recorded in both full and variable salinity (18-40) A decrease in one MNCR salinity scale to ‘Reduced' salinity (18-30 psu) may result in a decrease of Laminaria hyperborea sporophyte growth and Saccharina latissima. Resistance has been assessed as ‘Low’ and resilience as ‘Medium’. Therefore, the sensitivity of this biotope to a decrease in salinity has been assessed as ‘Medium’.

Peteiro & Freire (2013) measured Saccharina latissima growth from 2 sites, the first had maximal water velocities of 0.3 m/sec and the second 0.1 m/sec. At site 1 Saccharina latissima had significantly larger biomass than at site 2 (16 kg/m to 12 kg/m respectively). Peteiro & Freire (2013) suggested that faster water velocities were beneficial to Saccharina latissima growth. However, Gerard & Mann (1979) found Saccharina latissima productivity is reduced in moderately strong tidal streams (≤1m/sec) when compared to weak tidal streams (<0.5 m/sec). Despite these results where the substratum is unstable Saccharina lattissima can become the dominant canopy-forming kelp within tide swept conditions, as in IR.MIR.KT.XKTX (Connor et al., 2004).

Kregting et al. (2013) measured Laminaria hyperborea blade growth and stipe elongation from an exposed and a sheltered site in Strangford Lough, Ireland, from March 2009-April 2010. Maximal significant wave height (Hm0) was 3.67 & 2m at the exposed and sheltered sites, and maximal water velocity (Velrms) was 0.6 & 0.3 m/s at the exposed and sheltered sites respectively. Despite the differences in wave exposure and water velocity, there was no significant difference in Laminaria hyperborea growth between the exposed and sheltered sites. Therefore water flow was found to have no significant effect on Laminaria hyperborea growth at the observed range of water velocities.

Sensitivity assessment. IR.MIR.KT.XKT & IR.MIR.KT.XKTX are predominantly recorded from “Moderately strong” tidal streams (0.5-1.5 m/sec). Due to the range of tidal velocities that these biotopes are recorded within a change in the flow of between 0.1-0.2 m/sec would likely have no significant effect on Laminaria hyperborea or Saccharina latissima growth or productivity. Resistance has been assessed as ‘High’, resilience as ‘High’. Sensitivity has been assessed as ‘Not Sensitive’ at the benchmark level.

IR.MIR.KT.XKT & IR.MIR.KT.XKTX are shallow water biotopes, recorded predominantly from 0-5 m BCD. An increase in emergence will result in an increased risk of desiccation and mortality of the dominant kelp species (Laminaria hyperborea & Saccharina latissima). Removal of canopy-forming kelps has also been shown to increase desiccation and mortality of the understory macroalgae (Hawkins & Harkin, 1985). Several mobile species such as sea urchins, brittle stars and feather stars are likely to move away. However, providing that suitable substrata are present, the biotope is likely to re-establish further down the shore within a similar emergence regime to that which existed previously.

Sensitivity assessment. Resilience has been assessed as ‘Low’. Resistance as ‘Medium’. The sensitivity of this biotope to a change in emergence is considered as ‘Medium’.

Kregting et al. (2013) measured Laminaria hyperborea blade growth and stipe elongation from an exposed and a sheltered site in Strangford Lough, Ireland from March 2009 to April 2010. Wave exposure was found to be between 1.1. to 1.6 times greater between the exposed and sheltered sites. Maximal significant wave height (Hm0) was 3.67 & 2 m at the exposed and sheltered sites. Maximal water velocity (Velrms) was 0.6 & 0.3 m/s at the exposed and sheltered sites. Despite the differences in wave exposure and water velocity, there was no significant difference in Laminaria hyperborea growth between the exposed and sheltered site.

However, Pederson et al. (2012) observed Laminaria hyperborea biomass, productivity and density increased with greater wave exposure. At low wave exposure, Laminaria hyperborea canopy forming plants were smaller, had lower densities and had higher mortality rates. At low wave exposure, high epiphytic loading on Laminaria hyperborea was suggested to impair photosynthesis, nutrient uptake, and increase the drag of the host Laminaria hyperborea during extreme storm events. The morphology of kelp stipe and blades vary in different water flows and wave exposures water flow. In wave exposed areas, for example, Laminaria hyperborea develops a long and flexible stipe and this is probably a functional adaptation to strong water movement (Sjøtun et al., 1998). In addition, the lamina becomes narrower and thinner in strong currents (Sjøtun & Fredriksen, 1995).

Sensitivity assessment. Wave exposure is one of the principal defining features of kelp biotopes, and changes in wave exposure are likely to alter the relative abundance of the kelp species, understory community and hence the biotope. IR.MIR.KT.XKT & IR.MIR.KT.XKTX are recorded from wave sheltered sites so that an increase in wave exposure (e.g. to moderate or higher) is likely to result in modification of the community and loss of the biotope. However, a change in near shore significant wave height of 3-5% is unlikely to have any significant effect on IR.MIR.KT.XKT & IR.MIR.KT.XKTX. Resistance has been assessed as ‘High’, resilience as ‘High’ and sensitivity as ‘Not Sensitive’ at the benchmark level.

Chemical Pressures

Bryan (1984) suggested that the general order for heavy metal toxicity in seaweeds is: Organic Hg > inorganic Hg > Cu > Ag > Zn > Cd > Pb. Cole et al. (1999) reported that Hg was very toxic to macrophytes. Similarly, Hopkin & Kain (1978) demonstrated sub-lethal effects of heavy metals on Laminaria hyperborea gametophytes and sporophytes, including reduced growth and respiration. Sheppard et al. (1980) noted that increasing levels of heavy metal contamination along the west coast of Britain reduced species number and richness in holdfast fauna, except for suspension feeders which became increasingly dominant. Gastropods may be relatively tolerant of heavy metal pollution (Bryan, 1984). Echinus esculentus recruitment is likely to be impaired by heavy metal contamination due to the intolerance of its larvae. Echinus esculentus are long-lived and poor recruitment may not reduce grazing pressure in the short-term. Although macroalgae species may not be killed, except by high levels of contamination, reduced growth rates may impair the ability of the biotope to recover from other environmental disturbances.

Sporophytes of Saccharina latissima have a low intolerance to heavy metals, but the early life stages are more intolerant. The effects of copper, zinc and mercury on Saccharina latissima have been investigated by Thompson & Burrows (1984). They observed that the growth of sporophytes was significantly inhibited at 50 µg Cu /l, 1000 µg Zn/l and 50 µg Hg/l. Zoospores were found to be more intolerant and significant reductions in survival rates were observed at 25 µg Cu/l, 1000 µg Zn/l and 5 µg/l. Little is known about the effects of heavy metals on echinoderms. Bryan (1984) reported that early work had shown that echinoderm larvae were intolerant of heavy metals, e.g. the intolerance of larvae of Paracentrotus lividus to copper (Cu) had been used to develop a water quality assessment. Kinne (1984) reported developmental disturbances in Echinus esculentus exposed to waters containing 25 µg / l of copper (Cu). Sea-urchins, especially the eggs and larvae, are used for toxicity testing and environmental monitoring (reviewed by Dinnel et al. 1988). Taken together with the findings of Gomez & Miguez-Rodriguez (1999) above it is likely that echinoderms are intolerant of heavy metal contamination.

This pressure is Not assessed but evidence is presented where available.

Laminaria hyperborea and Saccharina latissima fronds, being predominantly subtidal, would not come into contact with freshly released oil but only to sinking emulsified oil and oil adsorbed onto particles (Birkett et al., 1998b). The mucilaginous slime layer coating of laminarians may protect them from smothering by oil. Hydrocarbons in solution reduce photosynthesis and may be algicidal. However, Holt et al. (1995) reported that oil spills in the USA and from the Torrey Canyon had little effect on kelp forests. Similarly, surveys of subtidal communities at a number sites between 1-22.5m below chart datum, including Laminaria hyperborea communities, showed no noticeable impacts of the Sea Empress oil spill and clean up (Rostron & Bunker, 1997). An assessment of holdfast fauna in Laminaria showed that although species richness and diversity decreased with increasing proximity to the Sea Empress oil spill, overall the holdfasts contained a reasonably rich and diverse fauna, even though oil was present in most samples (Sommerfield & Warwick, 1999). Laboratory studies of the effects of oil and dispersants on several red algae species, including Delesseria sanguinea (Grandy 1984; cited in Holt et al., 1995) concluded that they were all sensitive to oil/ dispersant mixtures, with little differences between adults, sporelings, diploid or haploid life stages. Holt et al. (1995) concluded that Delesseria sanguinea is probably generally sensitive to chemical contamination.

This pressure is Not assessed but evidence is presented where available.

O'Brian & Dixon (1976) suggested that red algae were the most sensitive group of macrophytes to oil and dispersant contamination (see Smith, 1968). Saccharina latissima has also been found to be sensitive to antifouling compounds. Johansson (2009) exposed samples of Saccharina latissima to several antifouling compounds, observing chlorothalonil, DCOIT, dichlofluanid and tolylfluanid inhibited photosynthesis. Exposure to Chlorothalonil and tolylfluanid was also found to continue inhibiting oxygen evolution after exposure had finished, and may cause irreversible damage.

Although Laminariahyperborea sporelings and gametophytes are intolerant of atrazine (and probably other herbicides) overall they may be relatively tolerant of synthetic chemicals (Holt et al., 1995; Johansson, 2009). Laminaria hyperborea survived within >55 m from the acidified halogenated effluent discharge polluting Amlwch Bay, Anglesey, albeit at low density. These specimens were greater than five years of age, suggesting that spores and/or early stages were more intolerant (Hoare & Hiscock, 1974). Patella pellucida was excluded from Amlwch Bay by the pollution and the species richness of the holdfast fauna decreased with proximity to the effluent discharge; amphipods were particularly intolerant although polychaetes were the least affected (Hoare & Hiscock, 1974). The richness of epifauna/flora decreased near the source of the effluent and epiphytes were absent from Laminaria hyperborea stipes within Amlwch Bay. The red alga Phyllophora membranifolia was also tolerant of the effluent in Amlwch Bay.

Smith (1968) also noted that epiphytic and benthic red algae were intolerant of dispersant or oil contamination due to the Torrey Canyon oil spill; only the epiphytes Crytopleura ramosa and Spermothamnion repens and some tufts of Jania rubens survived together with Osmundea pinnatifida, Gigartina pistillata and Phyllophora crispa from the sublittoral fringe. Delesseria sanguinea was probably to most intolerant since it was damaged at depths of 6m (Smith, 1968). Holt et al., (1995) suggested that Delesseria sanguinea is probably generally sensitive to chemical contamination. Although Laminaria hyperborea may be relatively insensitive to synthetic chemical pollution, evidence suggests that grazing gastropods, amphipods and red algae are sensitive. Loss of red algae is likely to reduce the species richness and diversity of the biotope and the understorey may become dominated by encrusting corallines; however, red algae are likely to recover relatively quickly.

Reduced oxygen concentrations can inhibit both photosynthesis and respiration in macroalgae (Kinne, 1977). Despite this, macroalgae are thought to buffer the environmental conditions of low oxygen, thereby acting as a refuge for organisms in oxygen depleted regions especially if the oxygen depletion is short-term (Frieder et al., 2012). A rapid recovery from a state of low oxygen is expected if the environmental conditions are transient. If levels do drop below 4 mg/l negative effects on these organisms can be expected with adverse effects occurring below 2mg/l (Cole et al., 1999).

Sensitivity Assessment. Reduced oxygen levels are likely to inhibit photosynthesis and respiration but not cause a loss of the macroalgae population directly. In addition, IR.MIR.KT.XKT & IR.MIR.KT.XKTX are tide swept so that any deoxygenation would be highly localised and transient. Resistance has been assessed as ‘High’, Resilience as ‘High’. Sensitivity has been assessed as ‘Not sensitive’ at the benchmark level.

Conolly & Drew (1985) found Saccharina latissima sporophytes had relatively higher growth rates when in close proximity to a sewage outlet in St Andrews, UK when compared to other sites along the east coast of Scotland. At St Andrews, nitrate levels were 20.22µM, which represents an approx 25% increase when compared to other comparable sites (approx 15.87 µM). Handå et al. (2013) also reported Saccharina latissima sporophytes grew approx 1% faster per day when in close proximity to Salmon farms, where elevated ammonium can be readily absorbed. Read et al. (1983) reported after the installation of a new sewage treatment works that reduced the suspended solid content of liquid effluent by 60% in the Firth of Forth, Saccharina latissima became abundant where previously it had been absent. Bokn et al. (2003) conducted a nutrient loading experiment on intertidal fucoids. Within 3 years of the experiment no significant effect was observed in the communities, however, 4-5 years into the experiment a shift occurred from perennials to ephemeral algae occurred. Although Bokn et al. (2003) focussed on fucoids the results could indicate that long-term (>4 years) nutrient loading can result in community shift to ephemeral algae species. Disparities between the findings of the aforementioned studies are likely to be related to the level of organic enrichment, however, could also be time dependent.

Johnston & Roberts (2009) conducted a meta-analysis, which reviewed 216 papers to assess how a variety of contaminants (including sewage and nutrient loading) affected 6 marine habitats (including subtidal reefs). A 30-50% reduction in species diversity and richness was identified from all habitats exposed to the contaminant types. Johnston & Roberts (2009) however also highlighted that macroalgal communities are relatively tolerant to contamination, but that contaminated communities can have low diversity assemblages which are dominated by opportunistic and fast growing species (Johnston & Roberts, 2009 and references therein).

Holt et al. (1995) suggest that Laminaria hyperborea may be tolerant of organic enrichment since healthy populations are found at ends of sublittoral untreated sewage outfalls in the Isle of Man. Increased nutrient levels e.g. from sewage outfalls, has been associated with increases in abundance, primary biomass and Laminaria hyperborea stipe production but with concomitant decreases in species numbers and diversity (Fletcher, 1996). Increases in ephemeral and opportunistic algae are associated with reduced numbers of perennial macrophytes (Fletcher, 1996). Increased nutrients may also result in phytoplankton blooms that increase turbidity.

Sensitivity assessment. Although nutrients may not affect kelps directly, indirect effects such as turbidity may significantly affect photosynthesis. Furthermore, nutrient enrichment may denude the associated community. However, the biotope is probably ‘Not sensitive’ (resistance is ‘High’ and resilience is ‘High) at the benchmark level (i.e. compliance with WFD criteria).

Conolly & Drew (1985) found Saccharina latissima sporophytes had relatively higher growth rates when in close proximity to a sewage outlet in St Andrews, UK when compared to other sites along the east coast of Scotland. At St Andrews, nitrate levels were 20.22 µM, which represents an approx 25% increase when compared to other comparable sites (approx 15.87 µM). Handå et al. (2013) also reported Saccharina latissima sporophytes grew approx 1% faster per day when in close proximity to Norwegian Salmon farms, where elevated ammonium can be readily absorbed. Read et al. (1983) reported after the installation of a new sewage treatment works that reduced the suspended solid content of liquid effluent by 60% in the Firth of Forth, Saccharina latissima became abundant where previously it had been absent. Bokn et al. (2003) conducted a nutrient loading experiment on intertidal fucoids. Within 3 years of the experiment no significant effect was observed in the communities, however, 4-5 years into the experiment a shift occurred from perennials to ephemeral algae occurred. Although Bokn et al. (2003) focussed on fucoids the results could indicate that long-term (>4 years) nutrient loading can result in community shift to ephemeral algae species. Disparities between the findings of the aforementioned studies are likely to be related to the level of organic enrichment, however, could also be time dependent.

Johnston & Roberts (2009) conducted a meta-analysis, which reviewed 216 papers to assess how a variety of contaminants (including sewage and nutrient loading) affected 6 marine habitats (including subtidal reefs). A 30-50% reduction in species diversity and richness was identified from all habitats exposed to the contaminant types. Johnston & Roberts (2009) however also highlighted that macroalgal communities are relatively tolerant to contamination, but that contaminated communities can have low diversity assemblages which are dominated by opportunistic and fast growing species (Johnston & Roberts, 2009).

Holt et al. (1995) suggest that Laminaria hyperborea may be tolerant of organic enrichment since healthy populations are found at ends of sublittoral untreated sewage outfalls in the Isle of Man. Increased nutrient levels e.g. from sewage outfalls, has been associated with increases in abundance, primary biomass and Laminaria hyperborea stipe production but with concomitant decreases in species numbers and diversity (Fletcher, 1996). Increases in ephemeral and opportunistic algae are associated with reduced numbers of perennial macrophytes (Fletcher, 1996). Increased nutrients may also result in phytoplankton blooms that increase turbidity.

Sensitivity assessment. Although nutrients may not affect kelps directly, indirect effects such as turbidity may significantly affect photosynthesis. Furthermore, organic enrichment may denude the associated community. Resistance has therefore been assessed as ‘Medium’, resilience as ‘High’. Sensitivity has been assessed as ’Low’.

Physical Pressures

All marine habitats and benthic species are considered to have a resistance of ‘None’ to this pressure and to be unable to recover from a permanent loss of habitat (resilience is ‘Very Low’). Sensitivity within the direct spatial footprint of this pressure is, therefore ‘High’. Although no specific evidence is described confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.

If rock substrata were replaced with sedimentary substrata this would represent a fundamental change in habitat type, which kelp species would not be able to tolerate (Birkett et al., 1998b). The biotope would be lost.

Sensitivity assessment. Resistance to the pressure is considered ‘None’, and resilience ‘Very Low’ or ‘None’. The sensitivity of this biotope to change from sedimentary or soft rock substrata to hard rock or artificial substrata or vice-versa is assessed as ‘High’

Low-level disturbances (e.g. solitary anchors) are unlikely to cause harm to the biotope as a whole, due to the impact’s small footprint. Commercial Laminaria hyperborea trawling occurs in Norway (see resilience). Trawling typically removes all large canopy-forming sporophytes (Svendsen, 1972; Christie et al., 1998). Saccharina latissima is commercially cultivated, however typically sporophytes are matured on ropes (Handå et al., 2013) and not directly extracted from the seabed. Thus evidence to assess the resistance of Saccharina latissima to in/direct harvesting or abrasion is limited.

Sensitivity assessment. Abrasion by passing trawls or harvesting of macroalgae is likely to remove a large proportion of the kelp biomass. However, Saccharina latissima has been shown to be an early colonizer (Kain, 1967; Lienaas & Christie, 1996) with the potential to recover rapidly, whereas Laminaria hyperborea may take 2-6 and the associated community 7->10 years to recover (Birkett et al., 1998b). Therefore, resistance has been assessed as ‘None’, resilience as ‘Medium’, and sensitivity as ‘Medium’.

Suspended Particle Matter (SPM) concentration has a linear relationship with sub-surface light attenuation (Kd) (Devlin et al., 2008). An increase in SPM results in a decrease in sub-surface light attenuation. Light availability and water turbidity are principal factors in determining kelp depth range (Birkett et al., 1998b). Light penetration influences the maximum depth at which kelp species can grow and it has been reported that laminarians grow down to depths at which the light levels are reduced to 1 percent of incident light at the surface. Maximal depth distribution of laminarians, therefore, varies from 100 m in the Mediterranean to only 6-7 m in the silt-laden German Bight. In Atlantic European waters, the depth limit is typically 35 m. In very turbid waters the depth at which Laminaria hyperborea is found may be reduced, or in some cases excluded completely (e.g. Severn Estuary), because of the alteration in light attenuation by suspended sediment (Birkett et al. 1998b; Lüning, 1990).

Laminaria spp. show a decrease of 50% photosynthetic activity when turbidity increases by 0.1/m (light attenuation coefficient =0.1-0.2/m; Staehr & Wernberg, 2009). An increase in water turbidity will likely affect the photosynthetic ability of Laminaria hyperborea and Laminaria ochroleuca and decrease Laminaria hyperborea abundance and density (see sub-biotope- IR.MIR.KR.Lhyp.Pk). Kain (1964) suggested that early Laminaria hyperborea gametophyte development could occur in the absence of light. Furthermore, observations from south Norway found that a pool of Laminaria hyperborea recruits could persist growing beneath Laminaria hyperborea canopies for several years, indicating that sporophyte growth can occur in light-limited environments (Christe et al., 1998). However in habitats exposed to high levels of suspended silts Laminaria hyperborea is out-competed by Saccharina latissima, a silt tolerant species, and thus, a decrease in water clarity is likely to decrease the abundance of Laminaria hyperborea in the affected area (Norton, 1978).

Sensitivity Assessment. Changes in water clarity are likely to affect photosynthetic rates and enable Saccharina latissima to compete more successfully with Laminaria hyperborea. A decrease in turbidity is likely to support enhanced growth (and possible habitat expansion) and is therefore not considered in this assessment. An increase in water clarity from clear to intermediate (10-100 mg/l) represents a change in light attenuation of ca 0.67-6.7 Kd/m, and is likely to result in a greater than 50% reduction in photosynthesis of Laminaria spp. Therefore, the dominant kelp species will probably suffer a significant decline and resistance to this pressure is assessed as ‘Low’. Resilience to this pressure is probably ‘Medium’ at the benchmark. Hence, this biotope is assessed as having a sensitivity of ‘Medium ‘to this pressure.

Smothering by sediment e.g. 5 cm material during a discrete event is unlikely to damage Laminaria hyperborea or Saccharina latissima sporophytes but may affect holdfast fauna, gametophyte survival, interfere with zoospore settlement and therefore recruitment processes (Moy & Christie, 2012). Given the short life expectancy of Saccharina latissima (2-4 years-(Parke, 1948)), IR.MIR.KT.XKT & IR.MIR.KT.XKTX is likely to be dependent on annual Saccharina latissima recruitment (Moy & Christie, 2012). Given the microscopic size of the gametophyte, 5 cm of sediment could be expected to significantly inhibit growth. However, laboratory studies showed that kelp gametophytes can survive in darkness for between 6-16 months at 8°C and would probably survive smothering by a discrete event. Once returned to normal conditions the gametophytes resumed growth or maturation within 1 month (Dieck, 1993). Intolerance to this factor is likely to be higher during the peak periods of sporulation and/or spore settlement.

IR.MIR.KT.XKT & IR.MIR.KT.XKTX are predominantly recorded in more than moderate tidal streams (>0.5 m/s), and deposited sediment is, therefore, likely to be removed within a few tidal cycles and effects likely to be transient.

Sensitivity assessment. Resistance has been assessed as ‘Medium’, resilience as ‘High’. Sensitivity has been assessed as ‘Low’.

Smothering by sediment e.g. 30 cm material during a discrete event is unlikely to damage Laminaria hyperborea or Saccharina latissima sporophytes but may affect holdfast fauna, gametophyte survival, interfere with zoospore settlement and therefore recruitment processes (Moy & Christie, 2012). Given the short life expectancy of Saccharina latissima (2-4 years-(Parke, 1948)), IR.LIR.K.LhypSlat is likely to be dependent on annual recruitment (Moy & Christie, 2012). Given the microscopic size of the gametophyte, 30 cm of sediment could be expected to significantly inhibit growth. However, laboratory studies showed that gametophytes can survive in darkness for between 6-16 months at 8°C and would probably survive smothering by a discrete event. Once returned to normal conditions the gametophytes resumed growth or maturation within one month (Dieck, 1993). Resistance to this factor is likely to be lower during the peak periods of sporulation and/or spore settlement.

Within the heavy sediment deposition, pressure sediment retention within the host habitat is likely to be longer than that of the light deposition pressure, however, IR.MIR.KT.XKT & IR.MIR.KT.XKTX are predominantly recorded in more than moderate tidal streams (>0.5 m/s), and deposited sediment is, therefore, likely to be removed within a few tidal cycles and effects likely to be transient.

Sensitivity assessment. To reflect the increase in time the sediment may be retained during a heavy deposition of sediment resistance has been assessed as ‘Medium’, resilience as ‘Medium’. Sensitivity has been assessed as ‘Medium’.

There is no evidence to suggest that anthropogenic light sources would affect Laminaria hyperborea or habitats. Shading of the biotope (e.g. by construction of a pontoon, pier etc) could adversely affect the biotope in areas where the water clarity is also low, and tip the balance to shade tolerant species, resulting in the loss of the biotope directly within the shaded area, or a reduction in laminarian abundance from forest to park type biotopes.

Sensitivity assessment. Resistance is probably 'Low', with a 'Medium' resilience and a sensitivity of 'Medium', albeit with 'low' confidence due to the lack of direct evidence

Not relevant. This pressure is considered applicable to mobile species, e.g. fish and marine mammals rather than seabed habitats. Physical and hydrographic barriers may limit the dispersal of spores. But spore dispersal is not considered under the pressure definition and benchmark.

Undaria pinnatifida has received a large amount of research attention as a major Invasive Non-Indigenous Species (INIS) which could out-compete native UK kelp habitats (see Farrell & Fletcher, 2006; Thompson & Schiel, 2012, Brodie et al., 2014; Hieser et al., 2014). Undaria pinnatifida was first recorded in the UK, Hamble Estuary, in June 1994 (Fletcher & Manfredi, 1995) and has since spread to a number of British ports. Undaria pinnatifida is an annual species, sporophytes appear in Autumn and grow rapidly throughout winter and spring during which they can reach a length of 1.65 m (Birkett et al., 1998b). Farrell & Fletcher (2006) suggested that native short-lived species that occupy similar ecological niches to Undaria pinnatifida, such as Saccharina latissima, are likely to be worst affected and out-competed by Undaria pinnatifida. Where present, an abundance of Undaria pinnatifida has corresponded to a decline in Saccharina lattissima (Farrel & Fletcher, 2006) and Laminaria hyperborea (Hieser et al., 2014).

In New Zealand, Thompson & Schiel (2012) observed that native fucoids could out-compete Undaria pinnatifida and re-dominate the substratum. However, Thompson & Schiel (2012) suggested the fucoid recovery was partially due to an annual Undaria pinnatifida die back, which as noted by Heiser et al. (2014) does not occur in Plymouth sound, UK. Undaria pinnatifida was successfully eradicated on a sunken ship in Clatham Islands, New Zealand, by applying a heat treatment of 70°C (Wotton et al., 2004), however, numerous other eradication attempts have failed, and as noted by Fletcher & Farrell (1998), once established Undaria pinnatifida resists most attempts at long-term removal. The biotope is unlikely to fully recover until Undaria pinnatifida is fully removed from the habitat, which as stated above is unlikely to occur.

Sensitivity assessment. Resistance to the pressure is considered ‘Low’, and resilience ‘Very low’, the non-native species would need to be removed before recovery can occur. The sensitivity of this biotope to the introduction of microbial pathogens is assessed as ‘High’.

There has been recent commercial interest in Saccharina lattisima as a consumable called ‘sea vegetables’ (Birkett et al., 1998b). Laminaria hyperborea is also extracted on a commercial scale in southern Norway, primarily for alginate (Werner & Kraan, 2004).

Commercial Laminaria hyperborea trawling occurs in Norway, during which Christie et al. (1998) report all large canopy-forming sporophytes are removed, sub-canopy sporophytes and understory community, however, remain intact. Saccharina latissima is commercially cultivated, however typically sporophytes are matured on ropes (Handå et al., 2013) and not directly extracted from the seabed. Thus evidence to assess the resistance of Saccharina latissima to direct harvesting is limited.

Sensitivity assessment. Resistance has been assessed as ‘None’, Resilience as ‘Medium’. Sensitivity has been assessed as ‘Medium’.

Incidental/accidental removal of Laminaria hyperborea and Saccharina latissima is likely to cause similar effects to that of direct harvesting; as such the same evidence has been used for both pressure assessments. There has been recent commercial interest in Saccharina latissima as a consumable called ‘sea vegetable’’ (Birkett et al., 1998b). Laminaria hyperborea is also extracted on a commercial scale in southern Norway, primarily for alginates (Werner & Kraan, 2004).

Commercial Laminaria hyperborea trawling occurs in Norway, during which Christie et al. (1998) report all large canopy-forming sporophytes are removed, sub-canopy sporophytes and understory community, however, remain intact. Saccharina latissima is commercially cultivated, however typically sporophytes are matured on ropes (Handå et al., 2013) and not directly extracted from the seabed. Thus evidence to assess the resistance of Saccharina latissima to direct harvesting is limited.

Sensitivity assessment. Resistance has been assessed as ‘None’, resilience as ‘Medium’ and sensitivity as ‘Medium’.

Bryan, G.W., 1984. Pollution due to heavy metals and their compounds. In Marine Ecology: A Comprehensive, Integrated Treatise on Life in the Oceans and Coastal Waters, vol. 5. Ocean Management, part 3, (ed. O. Kinne), pp.1289-1431. New York: John Wiley & Sons.

Erwin, D.G., Picton, B.E., Connor, D.W., Howson, C.M., Gilleece, P. & Bogues, M.J., 1990. Inshore Marine Life of Northern Ireland. Report of a survey carried out by the diving team of the Botany and Zoology Department of the Ulster Museum in fulfilment of a contract with Conservation Branch of the Department of the Environment (N.I.)., Ulster Museum, Belfast: HMSO.

Farrell, P. & Fletcher, R., 2006. An investigation of dispersal of the introduced brown alga Undaria pinnatifida (Harvey) Suringar and its competition with some species on the man-made structures of Torquay Marina (Devon, UK). Journal of Experimental Marine Biology and Ecology, 334 (2), 236-243.

Kitching, J., 1941. Studies in sublittoral ecology III. Laminaria forest on the west coast of Scotland; a study of zonation in relation to wave action and illumination. The Biological Bulletin, 80 (3), 324-337

Peteiro, C. & Freire, O., 2013. Biomass yield and morphological features of the seaweed Saccharina latissima cultivated at two different sites in a coastal bay in the Atlantic coast of Spain. Journal of Applied Phycology, 25(1), 205-213.

Sivertsen, K., 1997. Geographic and environmental factors affecting the distribution of kelp beds and barren grounds and changes in biota associated with kelp reduction at sites along the Norwegian coast. Canadian Journal of Fisheries and Aquatic Sciences, 54, 2872-2887.

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